New chemical substances for medicines or food additives are synthesized. Strong electromagnetic fields and magnetic fields are getting close to ourselves as we come to use electrical appliances such as personal computers or portable phones. To study effects of those new factors on us, statistical studies of human beings, and experiments using animals were conducted in associated with synthesized chemical substances, electromagnetic fields or magnetic fields.
However, results from the statistical studies of human beings were apt to be less reliable because desired experimental conditions were difficult to set. With conventional methods for studying the operation of chemical reagents on animals, the chemical reagents were injected into living individuals or administered orally. Consequently, one experiment needed at least one individual of animals. The experiments using animals were very costly, because the experiments needed a number of individuals to obtain reliable results, experimenters needed large equipments for keeping those individuals and had to carefully take care of them. Therefore, the reduction in number of animals to experiment was favorable.
It is desirable that experimenters can take extract tissues or cells from animals and keep the tissues or cells in appropriate conditions and observe the change in activities of the tissues or cells over time with the conditions changed. Methods or apparatus to keep tissues or cells in appropriate conditions, to change the conditions freely, and to permit observation of the change in activities of the tissues or cells over time have been desired to conduct experiments efficiently and at a low cost.